Cashew is a multipurpose tree of the Amazon that grows up to 15 m high. It has a thick and tortuous trunk with branches so winding that they frequently reach the ground. Cashew trees are often found growing wild on the drier sandy soils in the central plains of Brazil and are cultivated in many parts of the Amazon rainforest.

The cashew tree produces many resources and products. The bark and leaves of the tree are used medicinally, and the cashew nut has international appeal and market value as a food. Even the shell oil around the nut is used medicinally and has industrial applications in the plastics and resin industries for its phenol content. Then, there is the pseudo-fruit-a swollen peduncle that grows behind the real fruit that yields the cashew nut. The pseudo-fruit, a large pulpy and juicy part, has a fine sweet flavor and is commonly referred to as the "cashew fruit" or the "cashew apple." Fresh or frozen cashew fruit concentrate is as common a juice product in South American food stores as orange juice is in the United States. It is very perishable, however; therefore, no fresh cashew fruit is exported into the United States or Europe from South America.

The cashew nut is defined botanically as the fruit. It grows externally in its own kidney-shaped hard shell at the end of this pseudo-fruit, or peduncle. The nut kernel inside is covered with an inner shell, and between the two shells is a thick, caustic, and toxic oil called cardol. Cashew nuts must be cleaned to remove the cardol and then roasted or boiled to remove the toxins before they can be eaten.

TRIBAL AND HERBAL MEDICINE USES

Native to the northeast coast of Brazil, cashew was domesticated long before the arrival of Europeans at the end of the fifteenth century. It was "discovered" by European traders and explorers and first recorded in 1578. It was taken Brazil to India and East Africa, where it soon became naturalized. In sixteenth-century Brazil, cashew fruits and their juice were taken by Europeans to treat fever, sweeten breath, and "conserve the stomach."

The cashew tree and its nuts and fruit have been used for centuries by the indigenous tribes of the rainforest, and it is a common cultivated plant in their gardens. The Tikuna tribe in northwest Amazonia considers the fruit juice medicinal against influenza, and they brew a tea of leaves and bark to treat diarrhea. The Wayãpi tribe in Guyana uses a bark tea as a diarrhea remedy and colic remedy for infants. Tribes in Suriname use the toxic seed oil as an external worm medicine to kill botfly larvae under the skin. In Brazil, a bark tea is used as a douche for vaginal discharge and as an astringent to stop bleeding after a tooth extraction. A wine made from the fruit is used for dysentery in other parts of the Amazon rainforest. The fruit juice and a bark tea are very common diarrhea remedies throughout the Amazon today, used by curanderos and local people alike.

In Peruvian herbal medicine today, cashew leaf tea (called casho) is employed as a common diarrhea remedy; a bark tea is used as an antiseptic vaginal douche; and the seeds are used for skin infections. In Brazilian herbal medicine, the fruit is taken for syphilis and as a diuretic, stimulant, and aphrodisiac. A leaf tea is prepared as a mouthwash and gargle for mouth ulcers, tonsillitis, and throat problems and is used for washing wounds. An infusion and/or maceration of the bark is used to treat diabetes, weakness, muscular debility, urinary disorders, and asthma. The leaves and/or the bark is also used in Brazil for eczema, psoriasis, scrofula, dyspepsia, genital problems, and venereal diseases, as well as for impotence, bronchitis, cough, intestinal colic, leishmaniasis, and syphilis-related skin disorders. North American practitioners use cashew for diabetes, coughs, bronchitis, tonsillitis, intestinal colic, and diarrhea, and as a general tonic.

PLANT CHEMICALS

In addition to being delicious, cashew fruit is a rich source of vitamins, minerals, and other essential nutrients. It has up to five times more vitamin C than oranges and contains a high amount of mineral salts. Volatile compounds present in the fruit include esters, terpenes, and carboxylic acids. The bark and leaves of cashew are a rich source of tannins, a group of plant chemicals with documented biological activity. These tannins, in a 1985 rat study, demonstrated anti-inflammatory and astringent effects, which may be why cashew is effective in treating diarrhea. Anacardic acids are found in cashew, with their highest concentration is in the nutshells. Several clinical studies have shown that these chemicals curb the darkening effect of aging by inhibiting tyrosinase activity, and that they are toxic to certain cancer cells.

Cashew's antimicrobial properties were first documented in a 1982 in vitro study. In 1999, another study was published indicating it had good in vitro antibacterial activity against E. coli and Pseudomonas. Most recently, a 2001 study reported that a bark extract exhibited in vitro antimicrobial activity against 13 of 15 microorganisms tested. In 1999, researchers reported that cashew fruit exhibited antibacterial activity against the Gram-negative bacterium Helicobacter pylori, which is now considered to cause acute gastritis and stomach ulcers. Its effectiveness against leishmanial ulcers also was documented in two clinical studies. Finally, two studies (one in mice and the other in rats) in 1989 and 1998 document the protective quality of a leaf extract against lab-induced diabetes, although the extract did not act as hypoglycemic as some others, it did stabilize blood glucose levels near pretest levels.

CURRENT PRACTICAL USES

The different products produced from this tree offer a wide range of applications. The fruit is used to make highly nutritive snacks and juices, and fruit extracts are now being used in body-care products. Because of its high amount of vitamin C and mineral salts, cashew fruit is used as a catalyst in the treatment of premature aging of the skin and to remineralize the skin. It is also an effective scalp conditioner and tonic and is often used in shampoos, lotions, and scalp creams for the conditioning activity of its proteins and mucilage. Cashew leaf or bark tea is still widely used throughout the tropics as an effective diarrhea and colic remedy, considered gentle enough for children. Unfortunately, there are not many cashew products available in the U.S. market, besides of course, cashew nuts.

Traditional Preparation: The natural rainforest remedy for diarrhea and dysentery is 1/2 cup of a standard decoction of leaves and twigs, taken two or three times daily.

Contraindications: Skin contact with various parts of the fresh plant (leaves, bark, fruit, fruit oil) may cause dermatitis and to produce an allergic response. Cashew nuts and fruits have also been documented to cause food allergy reactions.

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